The present invention relates to superconducting switching/multiplexing/demultiplexing arrangements with a number of channels comprising a number of resonators. The invention also relates to filters for microwave signals comprising a number of resonators.
Still further the invention relates to a method for multiplexing/demultiplexing signals.
Multichannel communication systems microwave frequency multiplexers are needed. J. Uher et al., discloses filter in "Tuneable microwave and millimeter-wave passband filters", IEEE Trans. Microwave Theory, 1991, Vol. 39, No. 4, p. 643. If for example the communication systems operate in the frequency band of 1-3 GHz however, the filters get very bulky and their performance characteristics are not satisfactory for a number of reasons, e.g. narrow band, low loss, high power handling capability etc. is needed which cannot be provided to a sufficient extent. In order to design compact filters, resonators have been constructed which operate in two modes, i.e. dual mode resonators. U.S. Pat. No. 5,083,102 discloses a filter with a dual mode dielectric resonator which employs two azimuthally perpendicular degenerate modes. The tuning and coupling between orthogonal modes and dielectric resonators is achieved mechanically by the use of screws. Parallel-plate resonators operating in dual mode are also known. I. Bahl and P. Bharita, "Microstrip Antennas", Artech house, 1980 discusses the use of a notch to provide coupling between two uncoupled orthogonal modes of patch resonators. U.S. Pat. No. 5,172,084 shows a filter wherein two degenerate modes of a microstrip patch resonator are used. Two pairs of conducting leads are used to provide two degenerate modes which are azimuthally perpendicular and a special perturber is used to facilitate the coupling between orthogonal modes. However, the filter performance strongly suffer from parasitic surface modes propagating in the common substrate carrying the patches, i.e there are parasitic couplings between the resonators.
In general, all of the filters discussed above are too bulky in particular for communication systems which operate in the 1-3 GHz frequency band and they do not have ideal performance characteristics such as a narrow band, low loss, high power handling capabilities etc. None of the described ways of coupling does provide sufficient flexibility to be used in multichannel multiplexers etc.
From U.S. Pat. No. 4,881,051 a multiplexer of a branching filter type is known. The design of the multiplexer is very complex and it is based on a plurality of cavities with half- and/or quarter-cut dielectric single mode resonators. The multiplexer has 2-4 channels. In the case of narrow band channeled it is extremely critical to manufacturing tolerances. Moreover, since it is limited to a maximum of four channels, presumably it would not work for multichannel systems with a higher number of channels, or in other words either it would not work for more than four channels or it would be even more complex and in no way cost-effective. Still further, the multiplexer does not seem to be tuneable which means that it can not be used in systems wherein tunability is required.